Join per-column stats not scaled with estimated row count

### Describe the bug

For inner/left/right/full joins, estimate_join_cardinality concatenates both inputs' column statistics verbatim and never adjusts them to the estimated output cardinality:

- Count-like fields (null_count, distinct_count, byte_size, sum_value) aren't scaled to the join's fan-out/selectivity, so they can be inconsistent with the output num_rows.
- Outer joins don't NULL-pad the non-preserved side, even though the side-to-pad is already known (utils.rs:240-242).
- Equi-join key columns aren't intersected (min/max) or NDV-bounded (min(left_ndv, right_ndv)).

Related to #22743 but the general join case might be a bit more involved.

### To Reproduce

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### Expected behavior

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### Additional context

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